When most people think about body composition, they think about body fat percentage. But the other side of that equation — lean body mass — is arguably more important for day-to-day health, performance, and metabolic function. LBM is everything that is not fat: muscle, bone, organs, water, connective tissue. It determines your resting metabolic rate far more than total body weight does, anchors your protein requirements, and is used in clinical pharmacology to dose medications accurately in people at the extremes of body weight.
The Three Anthropometric Formulas
Three validated equations estimate LBM from height and weight without needing a body fat measurement. Each was derived from different reference populations and methods, which is why they sometimes give different results for the same person.
Boer formula (1984, American Journal of Physiology): Male: LBM = 0.407 × W + 0.267 × H − 19.2 Female: LBM = 0.252 × W + 0.473 × H − 48.3 James formula (1976, DHSS/MRC Report): Male: LBM = 1.1 × W − 128 × (W/H)² Female: LBM = 1.07 × W − 148 × (W/H)² Hume formula (1966, Journal of Clinical Pathology): Male: LBM = 0.3281 × W + 0.3393 × H − 29.5336 Female: LBM = 0.2969 × W + 0.4150 × H − 43.2933 W = weight in kg, H = height in cm All three differ by 1–3 kg for most adults; their average reduces the error.
Which Method Is Most Accurate?
A 2005 study by Janmahasatian et al. published in Clinical Pharmacokinetics compared these formulas against DEXA reference measurements and found that the Boer formula had the smallest bias across normal and obese body weights. The James formula can produce negative values for LBM in individuals with very high BMIs — a mathematical artefact — which limits its use in clinical settings. The Hume formula is accurate in normal-weight adults but less well validated in athletes with high muscle mass. For most practical purposes, averaging all three and flagging the spread gives a reliable estimate.
LBM for Protein Intake Targets
Protein requirements for muscle building, maintenance and retention are best expressed relative to lean body mass rather than total body weight. For a person with 30% body fat, basing protein intake on total weight would systematically overestimate needs compared to someone with 15% body fat at the same weight. The International Society of Sports Nutrition (ISSN) position stand recommends 1.4–2.0 g of protein per kg of body weight for exercising adults, which translates to roughly 1.6–2.4 g per kg of LBM for most people. A 2018 meta-analysis by Morton et al. (British Journal of Sports Medicine) found that protein intakes above about 1.62 g/kg/day total body weight did not further increase muscle gain in resistance-trained individuals.
Tip
If you are tracking body composition over time — whether cutting fat or building muscle — tracking LBM change alongside total weight is more informative than either figure alone. A diet phase that reduces total weight by 4 kg but preserves LBM is far more successful than one that cuts 4 kg but loses 2 kg of muscle. Re-measure body fat % every 4–6 weeks using the same method each time (skinfolds, tape method, or DEXA) and use the LBM calculator to see whether the change is going in the right direction.